1. Field of the Invention
The present disclosure relates to an Ethernet system having a dual-port, and more particularly to a switching device capable of solving a conflict caused by the dual-port in an Ethernet system having the dual-port.
2. Description of the Related Art
Recently, Ethernet communication system has been largely spread in the field of the industry since it has many advantages due to its high speed, its popularization and familiarization, and its ease of connection to an office network.
Furthermore, Ethernet technology using a dual-port is a communication scheme that is highlighted as a next generation industrial communication network since it has an embedded switch function to connect one module to another and comfortable and redundant functions of wiring.
In order to use a dual-port Ethernet, it is necessary to have a function to switch one port to another. Representative switching types in the art include Store and Forward type and Cut Through type, wherein whether a data frame is stored or not is fixed. For reference, a frame is a data unit including an IP address, a MAC address and a payload, and a packet is a data unit including the IP address and payload.
However, the Ethernet switching type in the art is not suitable for an industrial Ethernet since it does not consider a real time property and a Daisy Chained network.
FIGS. 1a and 1b are views illustrating a Store and Forward switching type in a general dual-port Ethernet system. First, since the Ethernet system has plural Ethernet ports, Port A and Port B, the system includes two media access controllers 1. That is, each port is connected to each media access controller (MAC) of Ethernet. Each media access controller 1 is connected to an upper layer device through buses, and exchanges a data frame with the upper layer device through buses.
In order to relay the data frame between the plural ports, each media access controller 1 is connected to the other media access controller with buffers interposed therebetween. The relayed data frame is stored in the buffer 5 where error in checked. After then, the data frame is relayed if there is no error in the data frame.
At this moment, the data frame received from the media access controller 1 of Ethernet at each port is relayed to another port or transferred to the upper layer device through buses after passing through the buffer 5. At this time, the data frame output from the media access controller is temporarily stored in the buffer and then the data frame is transmitted to a target media access controller to be relayed after all the data frame is stored in the buffer. At this moment, there occurs a transmission delay by a length of data frame as shown in FIG. 1b. 
FIGS. 2a and 2b are views illustrating a Cut Through switching type in a general dual-port Ethernet system.
First, since the Ethernet system has plural Ethernet ports, the system has two media access controller 1. That is, each port is connected to a media access controller of Ethernet, and the media access controller 1 is in turn connected to an upper layer device through buses and exchanges a data frame through buses.
In order to relay the data frame between plural ports, one media access controller 1 is connected to the other media access controller. The relayed data frame is transferred to the other media access controller, and then transmitted to the other port.
At this moment, the data frame received from the media access controller of Ethernet at each part is relayed to the other port or transferred to an upper layer device through buses. The data frame outputted from the media access controller 1 is transmitted to the target media access controller through buses. At this time, in the case that the data frame is relayed between ports while a data transmission is performed on the upper layer device, there occurs a conflict therebetween.
That is, generally, a relay delay by the length of data frame occurs in the Store and Forward type, and a conflict occurs in the Cut Through type in the case that data frame is relayed while data transmission is performed on the upper layer device.